The present invention is directed to removing material from a substrate or another layer of metal having one or more thin films formed on a substrate, specifically to a method for removing such material using spray (wet) etching, and more specifically to a process of removing both the field metal and the metal embedded in a substrate at substantially the same rate so as to leave a planar surface.
In the evolution of technology related to microelectronics, the use of metal conductive thin films formed on a substrate and the use of circuit patterns formed on or in vias (holes) of a substrate has become increasingly important. Numerous approaches have been developed for the fabrication of thin film assemblies for semi-conductors, printed circuits, etc. In the formation of such thin film assemblies various techniques have been developed to form circuit patterns, etc., either on an outer surface of a substrate or by grooves or vias in the substrate, and remove undesired material from substrate.
Generally, the removal of the undesired materials has been accomplished by placing masking material over the desired pattern and removing the undesired material by etching techniques. As a result, various etching processes and apparatus have been developed, as exemplified by U.S. Pat. Nos. 3,772,104 issued Nov. 13, 1973 to E. A. Chandross et al.; 4,317,698 issued Mar. 2, 1982 to J. T. Christol et al.; 4,700,993 issued Jan. 24, 1989 to E. F. Hagan; 4,976,810 issued Dec. 11, 1990 to S. Masuda et al.; and 5,002,627 issued Mar. 26, 1991 to A. Scheithauer et al.
In addition to the etching techniques for material removal, substantial efforts have been directed to mechanical, chemical, electrochemical, and chemical/mechanical polishing techniques. In many applications it is necessary to remove both the field metal and metal embedded in a substrate or in another layer of material formed on a substrate. For example, in the fabrication of planarized multi-level metal on a semiconductor substrate, it is desirable to remove both the field metal and the embedded circuit metal to produce a planar surface. Prior aprroaches producing the desired planar surfaces have been primarily directed to polishing techniques, or combinations of sputtering/ion milling, or other dry processes which are expensive, time consuming, and not satisfactory. An example of such a prior approach to forming desired planar surfaces is illustrated by the chem-mech polishing method of U.S. Pat. No. 4,944,836 issued Jul. 31, 1990 to K. D. Beyer et al.
While these prior polishing techniques, such as chemical-mechanical polishing (CMP) provided by above-referenced U.S. Pat. No. 4,944,836, has provided a technique for removal of copper, for example, and has produced substantially planar surfaces, a CMP process is very expensive to carry out (machine cost of $1,000,000.00), requires 5-10 minutes to remove one (1) micron of copper, and leaves the surface of the substrate (dielectric) not fully planar. Thus, there is a need for a more effective method of removing material from a substrate so as to provide a more planar surface on both the substrate and any circuit(s) embedded therein, and which is more cost effective as to equipment and time. The present invention fills that need by a spin-spray etching process for removing both the field metal and the embedded metal at substantially the same rate so as to leave a planar surface on both the metal pattern and the substrate (dielectric), and in a more cost effective manner.